CN108603455B

CN108603455B - Method and device for determining the air flow into the intake manifold of a two-stroke motor

Info

Publication number: CN108603455B
Application number: CN201680081337.7A
Authority: CN
Inventors: X.摩恩
Original assignee: Continental Automotive GmbH; Continental Automotive France SAS
Current assignee: Vitesco Technologies GmbH
Priority date: 2015-12-08
Filing date: 2016-11-18
Publication date: 2021-06-08
Anticipated expiration: 2036-11-18
Also published as: FR3044713A1; US10697386B2; WO2017097396A1; FR3044713B1; CN108603455A; US20180347496A1

Abstract

A method (31) for measuring the fresh air flow (MAF) into an intake manifold (12) of a two-stroke motor, said intake manifold (12) being located between a throttle box (11) and an intake system (13). The method uses a specific predictive model which depends on the fact that the two-stroke motor exhibits a weak load on the one hand and a medium or strong load on the other hand. The selection of a suitable model according to the load is obtained by means of a predetermined threshold value and two measures of absolute pressure obtained at the intake manifold at the crankshaft rotation angles in the vicinity of top and bottom dead center. Then, a pressure quotient is formed for each model, which is used to infer the flow of fresh air into the intake manifold.

Description

Method and device for determining the air flow into the intake manifold of a two-stroke motor

Technical Field

The present invention generally relates to a method for determining the flow of fresh air into the intake manifold of a two-stroke motor.

The invention also relates to a device for carrying out such a method.

Background

It is known to manipulate the fuel injection of an internal combustion engine by means of an electronic control system which calculates and commands the flow rates of the different fuel injectors according to values taken by a certain number of motor operating parameters.

Among the information necessary for controlling the injectors, the mass of fresh air entering the motor cylinder is listed. The air mass directly determines the quantity of fuel to be injected, in the case where the ratio between the air mass and the fuel quantity is in fact predefined for a given motor.

However, the mass of fresh air entering the cylinders of the internal combustion engine is difficult to measure directly, so that traditionally values of more available parameters are used, which enable recalculating more or less accurate values of this air mass according to the laws of thermodynamics and hydrodynamics.

For example, patent EP 1280988B 1 proposes a method for determining the air flow rate from the atmospheric pressure and the absolute pressure at the manifold measured in the intake manifold for a given crank angle.

The accuracy of this method is fully acceptable for a four-stroke motor, but it is less acceptable for a two-stroke motor.

In fact, it has been shown that for a two-stroke motor there is a non-linearity between the absolute pressure measured at the collecting main and the motor load. The method according to patent EP 1280988B 1 therefore cannot be applied in a reliable manner to all the loads that a two-stroke motor may present. More precisely, in a two-stroke motor exhibiting a weak load, the value of the absolute pressure measured at the intake manifold is considerably perturbed due to the more complex combustion conditions therein compared to in a four-stroke motor.

In a conventional manner, it is known to use an air flow meter to evaluate the quality of the air sent in a two-stroke motor. The use of flow meters is a too costly solution.

Disclosure of Invention

The present invention aims to eliminate or at least alleviate all or part of the limitations of the prior art solutions, in particular those presented above, by proposing a solution that enables the air flow of a two-stroke motor to be measured based on a measure of the absolute pressure at the manifold in the intake manifold for all the loads that the two-stroke motor may present.

The inventors have conducted experiments leading them to identify a correlation between the absolute pressure measured at the manifold and the quality of the fresh air entering the intake manifold. These experiments also lead the inventors to observe that these correlations are not identical in terms of the two-stroke motor exhibiting weak loads on the one hand and moderate or strong loads on the other hand. The inventors have therefore implemented a method for determining the air flow into the intake manifold of a two-stroke motor based on these observations.

To this end, a first aspect of the invention proposes a method for measuring the flow of fresh air into an intake manifold of a two-stroke motor, which is located between a throttle box and an intake system (such as intake by a piston skirt, by a flap or by a rotary valve). The method comprises the following steps:

selecting a predetermined first and second crankshaft rotation angle at which an absolute pressure at the collecting main should be obtained in the intake collecting main;

acquiring a first insulation pressure in the intake manifold at a predetermined first crankshaft rotation angle near top dead center;

acquiring a second absolute pressure in the intake manifold at a predetermined second crankshaft rotation angle near bottom dead center;

detecting whether the motor is operating below or above a predetermined load threshold based on the first absolute pressure value, the second absolute pressure value, and the atmospheric pressure;

and when the motor is operating below a predetermined load threshold:

determining the flow rate of fresh air in the intake manifold on the basis of a predetermined characteristic straight line, said predetermined characteristic straight line describing at least a linear relationship between, on the one hand, the rise in pressure in the intake manifold between top dead center and bottom dead center and, on the other hand, the measured amount of fresh air circulating between the throttle box and the intake system when the intake system is closed.

This has the advantage of simplicity, since the method enables the application of a suitable predetermined model to the load of the two-stroke motor, and this is based on only two absolute pressure measurements at the intake manifold. The use of a flow meter is not necessary and the estimation of the air flow is accurate because it is adapted to the load of the two-stroke motor.

In a first implementation, the method comprises the steps consisting in: for a given motor speed, a predetermined load threshold is determined based on the first and second absolute pressures. This implementation enables a simple estimation of the load of the two-stroke motor to be obtained. Furthermore, since the implementation is not based on angle information at the throttle box, it can be used in the absence of throttle angle information.

In a second implementation, the method comprises the steps consisting in:

forming a first quotient (quotient) based on the first absolute pressure and the atmospheric pressure;

forming a second quotient based on the second absolute pressure and the atmospheric pressure; and

detecting whether the motor is operating below or above a predetermined load threshold based on the first and second quotients.

This has an efficiency advantage because the quotient is dependent on atmospheric pressure, so that the invention can also be implemented at altitude with little or no correction.

In a second example of implementation, when the motor is operating below a predetermined load threshold, the method comprises the steps consisting in:

forming a third quotient based on the first quotient and the second quotient; and

for a given motor speed, the flow rate of fresh air in the intake manifold is determined on the basis of a predetermined characteristic straight line which describes at least a linear relationship between the third quotient on the one hand and the measured amount of fresh air which circulates between the throttle box and the intake system when the intake system is closed on the other hand.

In another example of the second implementation, when the motor is operating above a predetermined load threshold, the method comprises the steps consisting in: for a given motor speed, the flow rate of fresh air in the intake manifold is determined on the basis of a predetermined characteristic curve which describes a relationship between the first quotient on the one hand and the measured amount of fresh air which circulates between the throttle box and the intake system when the intake system is closed on the other hand.

In a third implementation, the method comprises the steps consisting in: the predetermined first and second crankshaft rotation angles are selected in a range of about 30 degrees or so.

In an example of the third implementation, the method comprises the steps consisting in:

the predetermined first and second crankshaft rotation angles are selected in a range around about 30 degrees, preferably at 30 degrees for the predetermined first angle and at 180 degrees for the predetermined second angle.

These values have been measured since they are relevant for two-stroke motors.

In a second aspect, the invention relates to a method for retrofitting an electronic control module prepared for use with a two-stroke motor having an intake manifold with a pressure sensor between a throttle box and an intake system. Said improved method is characterized in that it comprises the following steps: the flow of fresh air into the intake manifold is measured according to the method according to the first aspect.

In a third aspect, the invention also relates to an electronic Control module (or ECU for an "Engine Control Unit" in english) prepared for use with a two-stroke motor having an intake manifold between a throttle box and an intake system, the intake manifold having a pressure sensor, the electronic Control module being adapted for measuring the flow of fresh air into the intake manifold according to the method according to the first aspect.

A fourth aspect of the invention relates to a vehicle comprising an electronic steering module according to the third aspect of the invention.

A fifth aspect of the invention relates to the use of the electronic steering module of the third aspect for detecting combustion instabilities in a two-stroke motor.

Finally, in a sixth and final aspect, the invention relates to the use of the electronic steering module of the third aspect in combination with a method or a device adapted for determining the flow of fresh air in a collecting main based on angular information at a throttle box for detecting a malfunction of an air line of a two-stroke motor.

Drawings

Other features and advantages of the invention will also appear upon reading the ensuing description. The description is purely illustrative and should be read in relation to the accompanying drawings, in which:

figure 1 is a schematic representation of an air intake circuit (circuit) of a two-stroke motor;

fig. 2 is a step diagram illustrating an embodiment of the method for determining the flow rate of air into the intake manifold of a two-stroke motor according to the invention.

In the drawings, like reference characters designate like or similar elements throughout the several views. For clarity reasons, the elements represented are not to scale relative to each other unless mentioned to the contrary.

Detailed Description

Fig. 1 schematically shows an air intake circuit 10 of a known type for a two-stroke motor (not shown).

The air intake line 10 comprises a shutter, called throttle box 11, positioned between an air filter (not represented) and an intake manifold 12 (manifold in english), such as illustrated by fig. 1. The throttle box 11 comprises an air intake duct and a throttle valve in the form of a generally flat plate rotatably mounted in the duct. The air intake in the intake manifold 12 is regulated according to the angular positioning of the throttle in the duct of the throttle box 11. The intake manifold 12 is located between the throttle box 11 and an intake system 13 arranged inside the compressor shell 14. For example, the intake system may be an intake through a piston skirt, with a flap, or through a rotary valve. The intake manifold 12 comprises an absolute pressure sensor of known type, which enables the absolute pressure at the manifold to be measured in the intake manifold 12. For example, the pressure sensor may be a pressure sensor such as those used in an intake line of a four-stroke motor, which have a narrow range of use below atmospheric pressure.

As indicated above, the inventors conducted experiments leading them to identify the correlation between the absolute pressure measured at the manifold and the quality of the fresh air entering the intake manifold, depending on the fact that the two-stroke motor presents a weak load on the one hand and a medium or strong load on the other hand.

In fact, the aim is to make a model for filling with fresh air based on pressure information.

To this end, numerous tests have been implemented. In particular, the following have been varied: the amount of fuel injected, spark advance, compression ratio of the motor, positioning of intake and exhaust ports, and environmental conditions such as temperature. For each of the changes, or combinations of changes, the fresh air flow and absolute pressure have been measured at multiple locations based on pressure sensors. In particular, the pressure sensor has been positioned downstream of the throttle box 11, in the compressor casing 14, in the motor cylinder or in the exhaust line.

Based on the metric information described above, the inventors concluded that: the simple acquisition of the pressure does not enable to correctly infer the fresh air flow rate, since no monotonicity between the measured pressure and the measured fresh air flow rate is observed for all the loads that the two-stroke motor may present.

Based on this recognition, the inventors have developed a specific predictive model which depends on the fact that the two-stroke motor exhibits a weak load on the one hand and a medium or strong load on the other hand. The selection of a suitable model according to the load is obtained by means of a predetermined threshold value and two measures of the absolute pressure obtained at the intake manifold at the crankshaft rotation angles in the vicinity of top and bottom dead center. Then, a pressure quotient is formed for each model, which is used to infer the flow of fresh air into the intake manifold 12.

Fig. 2 schematically illustrates the main steps of a method 100 according to the invention for determining the flow of air into the intake manifold 12 of fig. 1. The method is implemented, for example, in the form of computer program instructions stored and executed in an electronic manipulation module (not shown).

At step 101, a value of a first absolute pressure MAP in the intake manifold 12 is acquired at a predetermined first crankshaft rotation angle in the vicinity of top dead center (PMH). For example, the predetermined first angle is fixed at a crank angle of 30 degrees near the PMH.

At step 102, a value of a second absolute pressure MAP _ UP in the intake manifold 12 is acquired at a predetermined second crank rotation angle in the vicinity of bottom dead center (PMB). For example, the predetermined second angle is fixed at a crankshaft angle of 180 degrees near the PMB.

According to the invention, the predetermined first crankshaft rotational angle is selected such that it differs from the predetermined second crankshaft rotational angle. Furthermore, the selection of the predetermined first crankshaft rotational angle and the predetermined second crankshaft rotational angle may be implemented in a range around approximately 30 degrees around PMH or PMB, respectively.

After step 102, the load state of the two-stroke motor is determined according to the value of the absolute pressure MAP, the value of the absolute pressure MAP _ UP, and the atmospheric pressure AMP, as per steps 103 and 104.

At step 103, the atmospheric pressure AMP is determined by means of a method of known type for determining atmospheric pressure. For example, the atmospheric pressure AMP may be determined based on the value of the absolute pressure MAP _ UP. In fact, since the value of pressure signal MAP _ UP is obtained when the crankshaft is at PMB, signal MAP _ UP represents the pressure upstream of the throttle box. In a particular implementation, a low pass filter is used to update the atmospheric pressure AMP, the activation of which is determined by the rotational speed and load parameters of the motor (even the first quotient PQ _ AMP, e.g., at step 104). The inputs to the low-pass filter are then the values of the absolute pressure signal MAP UP that are modified by the MAP, which are those that enable activation of the filter, i.e. the motor speed and the load. In an example, the correction may be limited to a low value, e.g. 20mbar, at many operating points of the motor.

At step 104, a first quotient PQ _ MAP is formed based on the values of MAP and AMP. For example, the quotient PQ _ MAP corresponds to the ratio MAP/AMP. Further, at step 104, a second quotient PQ _ MAP _ UP is formed based on the values of MAP _ UP and AMP. For example, the quotient PQ _ MAP _ UP corresponds to the ratio MAP _ UP/AMP. Finally, still at step 104, a load index IC for the two-stroke motor is determined based on the quotients PQ _ MAP and PQ _ MAP _ UP. For example, the load index IC corresponds to the sum of the quotients PQ _ MAP and PQ _ MAP _ UP.

After step 104, it is determined whether the two-stroke motor is operating below or above the predetermined load threshold S according to

steps

105 and 106. Within the framework of the invention, the predetermined load threshold S makes it possible to divide the operating mode of the two-stroke motor into two parts according to the fact that it exhibits a weak load on the one hand and a medium or strong load on the other hand. Furthermore, the inventors have found that the predetermined load threshold S varies in accordance with the motor speed N. Thus, the predetermined load threshold S may be different for each motor speed N.

At step 105, the speed N of the two-stroke motor is determined by means of a method for determining the speed of the motor of known type. For example, a known type of motor speed sensor or a known type of motor speed estimator may be used. Further, at step 105, a predetermined load threshold S corresponding to the motor speed N is determined. For example, the predetermined threshold S for a given motor rotation speed may be determined based on a correspondence table stored in advance in the memory.

In step 106, it is determined whether the two-stroke motor is operated below or above the threshold S by comparing the load index IC with the threshold S.

Then, when the load index IC is below the threshold S, the method 100 continues at step 107, and when the load index IC is above the threshold S, the method 100 continues at step 109.

At step 107, a third quotient PQ _ BDC is formed based on the quotient PQ _ MAP _ UP and PQ _ MAP. For example, the quotient PQ _ BDC corresponds to the ratio (PQ _ MAP _ UP-PQ _ MAP)/(1-PQ _ MAP).

At step 108, the fresh air flow rate MAF in the intake manifold 12 is determined based on a predetermined characteristic straight line MAF _ BDC describing at least a linear relationship between the quotient PQ _ BDC and the fresh air flow rate at the intake manifold 12. More precisely, the straight line MAF _ BDC exhibits a predetermined slope describing a linear relationship between, on the one hand, the rise in pressure in the intake manifold between top dead center and bottom dead center and, on the other hand, the measured amount of fresh air circulating between the throttle box and the intake system when the latter is closed. In fact, the inventors have found that there is a linear correlation between the quotient PQ _ BDC and the flow MAF when the two-stroke motor exhibits a weak load. The inventors have also found that the correlation may be piecewise linear. In this case, the predetermined characteristic straight line MAF _ BDC is composed of a plurality of segments.

In a particular implementation of the invention, the pressure rise in the intake manifold is only taken into account for the determined region located between PMH and PMB. For example, a method may be envisaged that is based on a measure of pressure at the PMH and a measure of pressure gradient at 100 ° after the PMH. Equivalent results to solutions such as those described will then be obtained.

The above described correlation is due in particular to the specific operation of the two-stroke motor over a complete revolution. In fact, in the first motor stroke, the piston of the motor cylinder is at the top dead center and the lower casing is at its maximum volume level. In fact, at this moment, in the example, a shutter at the intake system 13 opens to make the lower casing suck the air coming from the intake line 10. Then, in a second motor stroke, the piston is lowered for compressing the mixture in the lower housing. At the same time, the shutter of the air intake system is closed so that no more air enters the lower cabinet. Thus, between the passage from top dead center to bottom dead center, the opening of the throttle box will cause a rise in pressure due to the intake system being closed, which enables the quantity of fresh air entering the intake manifold to be characterized.

Furthermore, the inventors have found that the correlation depends on the motor speed. The flow MAF for a given motor speed can thus be determined, for example, on the basis of a correspondence table stored in advance in a memory, describing the relationship between the quotient PQ _ BDC and the flow MAF.

At step 109, the fresh air flow MAF in the intake manifold is determined based on a predetermined characteristic MAF MAP, which describes the relationship between the quotient PQ _ MAP and the fresh air flow at the intake manifold 12. In fact, the inventors have found that there is a correlation between the quotient PQ _ MAP and the flow MAF when the two-stroke motor exhibits a medium or strong load. Furthermore, the inventors have found that the correlation depends on the motor speed. The flow MAF for a given motor speed may thus be determined, for example, on the basis of a correspondence table stored in advance in a memory, describing the relationship between the quotient PQ _ MAP and the flow MAF.

After

steps

108 and 109, the fresh air flow MAF is corrected in an optional manner based on the temperature T at the intake of the two-stroke motor and the atmospheric pressure AMP. For example, the atmospheric pressure AMP obtained at step 103 above may be used.

At step 110, the temperature T at the cylinder of the two-stroke motor is determined by means of a method for determining the air temperature of the known type. For example, a temperature sensor of a known type may be used.

At step 111, a correction CORR for fresh air flow MAF is determined based on temperature T and barometric pressure AMP by means of a correction method. In the implementation of the correction method, the correction is based on a predetermined correspondence tableA correction corr (T) is determined which depends on the temperature T. Then, a correction CORR _ AMP (N, AMP) depending on the motor rotation speed and the atmospheric pressure is determined based on a predetermined correspondence table. In an example, corr (t) is defined by the following equation: CORR (T) = T^0.8Wherein T is expressed in degrees Kelvin. In another example, the correction CORR _ AMP (N, AMP) is equal to zero.

Finally, at step 112, a corrected fresh air flow MAF — CORR is determined by applying a correction CORR to the fresh air flow MAF. In the example, the corrected fresh air flow MAF — CORR is defined by the following equation:

MAF_CORR = CORR(T) * (MAF * AMP + COR_AMP(N, AMP))。

the method 100 may be implemented in an electronic steering module ("ECU" in english) of a vehicle including a two-stroke motor, such as a watercraft, a snowmobile, or any ground-type motorcycle. The electronic control module comprises, for example, at least one processor and at least one memory, in which a computer program is stored. The program comprises a set of program code instructions which, when executed by a processor, implement different steps of the method 100 such as described above. In a variant, the electronic manipulation module comprises hardware devices, such as one or more programmable logic circuits of the FPGA, PLD or the like type, and/or one or more application-specific integrated circuits (ASICs) adapted to implement all or part of the steps of the method 100.

A combination of such hardware means with one or more computer programs is also possible.

In other words, the electronic manipulation module comprises a set of means configured for implementing the method 100 in software (specific computer program product) and/or hardware (FPGA, PLD, ASIC, etc.).

The present invention presents numerous advantages. For example, the inventors have observed that the variability of the value of the absolute pressure MAP makes it possible to deduce therefrom the instability of the motor in terms of combustion. Thus, when the two-stroke motor is operating under a weak load and a variation deviation, such as a root mean square deviation, of the value of the absolute pressure MAP greater than a predetermined threshold is observed, it is then possible to envisage correcting the richness of the mixture or the spark advance in order to stabilize the combustion. Furthermore, the observation of the value of the absolute pressure MAP also enables detection of combustion misfire. In fact, the inventors have observed that the value of the absolute pressure MAP is relatively stable when there is little misfire. Therefore, if a sudden change in the value of the absolute pressure MAP is observed, this may be an indication of a combustion misfire, unstable combustion, or control correction element. Therefore, when unstable combustion is detected, it will be conceivable to correct the control parameters (such as injection and ignition). It would also be possible to increase the injection time, or increase the spark advance, for example. It is thus possible to monitor the occurrence of pressure peaks on the basis of the value of the absolute pressure MAP and to obtain new information about the combustion state. This is an advantage over what can be obtained in a four-stroke motor where combustion instability does not necessarily imply pressure instability.

The invention may also be coupled to a method or apparatus adapted to determine the fresh air flow rate in the collecting main based on angle information at the throttle box. For example, if there is a significant difference between the fresh air flow rate obtained from the throttle angle information and the fresh air flow rate obtained according to the present invention, an air leak or malfunction at the exhaust shutter may be detected. In another example, the dysfunction of the throttle angle information may be mitigated by the redundant use of the present invention.

The present invention has been described and illustrated in the detailed description and in the figures of the accompanying drawings. However, the invention is not limited to the implementation forms thus presented. Other variations and embodiments can be inferred and implemented by those skilled in the art upon reading the present description and the accompanying drawings.

In the claims, the term "comprising" does not exclude other elements or steps. The word "a" or "an" does not exclude a plurality. A single processor or multiple other units may be used to implement the invention. The different features presented and/or claimed may be advantageously combined. Their presence in the description or in different dependent claims does not exclude this possibility. Finally, the reference signs in the figures accompanying them shall not be construed as limiting the scope of the invention.

Claims

1. A method (100) for measuring the flow rate (MAF) of fresh air into an intake manifold (12) of a two-stroke motor, the intake manifold (12) being located between a throttle box (11) and an intake system (13), characterized in that the method (100) comprises the steps of:

selecting a predetermined first crankshaft rotation angle and a predetermined second crankshaft rotation angle at which the absolute pressure at the collecting main should be obtained in the intake collecting main (12);

acquiring (101) a first absolute pressure (MAP) at the manifold in the intake manifold (12) at a predetermined first crankshaft rotation angle in the vicinity of top dead center (PMH);

acquiring (102) a second absolute pressure (MAP UP) at the manifold in the intake manifold (12) at a predetermined second crankshaft rotation angle in the vicinity of bottom dead center (PMB);

detecting (103, 104, 105, 106) whether the motor is operating below a predetermined load threshold (S) or above the predetermined load threshold (S) depending on the value of the first absolute pressure (MAP), the value of the second absolute pressure (MAP UP) and the atmospheric pressure (AMP);

and when the motor is operating below a predetermined load threshold (S):

-determining the flow rate (MAF) of fresh air in the intake manifold (12) on the basis of a predetermined characteristic straight line (MAF _ BDC) describing at least a linear relationship between, on the one hand, the rise in pressure in the intake manifold (12) between top dead center (PMH) and bottom dead center (PMB) and, on the other hand, the measured amount of fresh air circulating between the throttle box (11) and the intake system (13) when the intake system (13) is closed.

2. The method (100) according to claim 1, characterized in that the method further comprises the steps of:

forming a first quotient (PQ _ MAP) based on the first absolute pressure (MAP) and the atmospheric pressure (AMP);

forming a second quotient (PQ _ MAP _ UP) based on the second absolute pressure (MAP _ UP) and the atmospheric pressure (AMP); and

detecting (106) whether the motor is operating below or above a predetermined load threshold (S) based on the first and second quotient.

3. Method (100) according to claim 2, characterized in that when the motor is operating below a predetermined load threshold (S), the method further comprises the steps of:

forming (107) a third quotient (PQ _ BDC) based on the first quotient (PQ _ MAP) and the second quotient (PQ _ MAP _ UP); and

-determining (108), for a given motor speed (N), the flow rate (MAF) of fresh air in the intake manifold (12) based on a predetermined characteristic straight line (MAF _ BDC) describing at least a linear relationship between, on the one hand, the third quotient (PQ _ BDC) and, on the other hand, the measured amount of fresh air circulating between the throttle box (11) and the intake system (13) when the intake system (13) is closed.

4. Method (100) according to any one of claims 2 or 3, characterized in that when the motor is operating above a predetermined load threshold (S), the method further comprises the steps of:

-determining (109), for a given motor speed (N), a flow rate (MAF) of fresh air in the intake manifold (12) based on a predetermined characteristic curve (MAF MAP) describing a relationship between, on the one hand, a first quotient (PQ MAP) and, on the other hand, a measured amount of fresh air circulating between the throttle box (11) and the intake system (13) when the intake system (13) is closed.

5. The method (100) according to any one of claims 1 to 3, characterized in that it further comprises the steps of:

selecting the predetermined first crankshaft rotation angle and the predetermined second crankshaft rotation angle in a range around 30 degrees.

6. The method (100) according to claim 5, characterized in that the predetermined first crankshaft rotation angle is fixed at 30 degrees near top dead center (PMH) and the predetermined second crankshaft rotation angle is fixed at 180 degrees near bottom dead center (PMB).

7. A method for retrofitting an electronic steering module prepared for use with a two-stroke motor having an intake manifold (12) between a throttle box (11) and an intake system (13), the intake manifold (12) having a pressure sensor, the method being characterized in that it comprises the steps of: measuring the flow rate (MAF) of fresh air into an intake manifold (12) according to a method according to any one of claims 1 to 6.

8. Electronic steering module prepared for use with a two-stroke motor having an intake manifold (12) between a throttle box (11) and an intake system (13), the intake manifold (12) having a pressure sensor, the electronic steering module being adapted to measure the flow rate (MAF) of fresh air into the intake manifold (12) according to the method of any one of claims 1 to 6.

9. A vehicle, characterized in that it comprises an electronic steering module according to claim 8.

10. Use of an electronic steering module according to claim 8 for detecting combustion instability of a two-stroke motor.

11. Use of an electronic steering module according to claim 8 for detecting a malfunction of an air line of a two-stroke motor in combination with a method or a device adapted for determining a fresh air flow in a collecting main based on angular information at a throttle box.